The broad, long-term objectives of the proposed research are to characterize, quantify and determine the significance of acyl-carrier proteins in the production of lipids by the symbiotic dinoflagellate algae (zooxanthellae) of tropical marine coelenterates. The proposed research will examine one of the most important biochemical interactions in these symbioses: the production of lipid from carbon photosynthetically fixed by zooxanthellae and the utilization of this lipid by the coelenterate host. Symbiotic coelenterates are simple organisms that have been used as model systems to study basic biomedical processes, such as calcification and histocompatibility. Symbiotic coelenterates are also and ideal model system for the study of lipid metabolism. The proposed research will focus on the role of acyl-carrier proteins in the production and export of lipid from zooxanthellae. Specific aims of the research include the following: A) Determination of the levels of free and acylated acyl-carrier proteins and testing the hypothesis that rates of lipid synthesis will correlate with level of ACP in the zooxanthellae. B) Determine if zooxanthellae have single isoforms of ACP like all other known unicellular organisms and test the hypothesis that when in symbiosis zooxanthellae have multiple ACP isoforms. C) Determine if the coelenterate host can control the lipid metabolism of its symbiotic algae and teat the hypotheses that environmental stress and reproductive status alter levels of ACP in zooxanthellae and the metabolic fate of zooxanthellae-derived lipids. This research will increase our general understanding of both lipid metabolism and metabolic interchange in unicellular as well as multicellular organisms.